This invention relates to a light-sensitive silver halide photographic material feasible for high speed processing. Particularly, it relates to a light-sensitive silver halide photographic material having high sensitivity and also having excellent pressure resistance and graininess even when subjected to an ultra rapid processing.
In recent years, light-sensitive silver halide photographic materials have been consumed in such quantities that go on increasing. For this reason, there is an increase in the number of sheet for the processing of light-sensitive silver halide photographic materials, and it has been needed to carry out the processing more rapidly, in other words, to increase processing quantities in a given time.
The above trend is also seen in the field of X-ray light-sensitive materials, for example, of X-ray films for medical use. More specifically, with a rapid increase in the frequency of diagnosis to be caused by encouragement of periodical health examinations, it is attempted to diagnose more accurately, thereby increasing check items and thus increasing the number of sheet for the X-ray photography.
On the other hand, it is also necessary to give notice of results of diagnosis as soon as possible, to those who have been diagnosed.
That is, there are strong demands for carrying out the processing more rapidly than ever to facilitate the diagnosis. In particular, in angiography, perioperative photography or the like, it is essentially necessary to look at photographs in a time as short as possible.
In order to satisfy the above demands in the medical field, it is necessary to promote the automatization (in photography, conveyance, etc.) of the diagnosis, and also to process X-ray films more rapidly.
However, the ultra rapid processing causes problems such that (a) density is insufficient (i.e., decrease in sensitivity, contrast and maximum density), (b) fixing can not be sufficiently carried out, (c) water washing of films may become insufficient, (d) drying of films may become insufficient, and so forth. Moreover, the insufficient fixing and insufficient water washing may cause a change in tone during storage of films to lower image quality.
A means for solving these problems is to decrease the amount of gelatin. However, decrease in the amount of gelatin tends to bring about troubles such as coating unevenness and coating streaks. Also, films with less gelatin may produce problems such that, when films rub each other or films are rubbed by other materials, the so-called abrasion blackening may become liable to occur after the processing to form a portion having higher density than other portions, i.e., the so-called abrasion blackening.
Ultra rapid processing has been sought after as mentioned above. In the present specification, the ultra rapid processing is meant to be a processing for 20 seconds to 60 seconds in total of the time during which a top end of a film is first inserted to an automatic processor, and then passes through a developing tank, a gangway, a fixing tank, a gangway, a washing tank, a gangway and a drying spot, and thereafter the top end of the film comes out of the drying spot [in other words, the quotient (sec) obtained by dividing the total length (m) of a processing line by the line conveyor speed (m/sec)]. The reason why the time for the gangways is included is, though well known in the present industrial field, that a processing solution used in a step preceding thereto may swell also at a gangway and a processing step is considered to substantially proceed thereat.
To promote the rapid processing, it becomes very important to control the surface tension and viscosity of coating solutions used for forming an outermost layer and a layer adjacent thereto which constitute a light-sensitive silver halide photographic material. In particular, a technique for improving the viscosity of a coating solution is disclosed in Japanese Unexamined Patent Publications No. 115214/1977, No. 1350/1979 and No. 108566/1981 as a bead coating technique. Also, a great number of efforts has been made on the formation of better photographic layers according to other various methods. For example, as conditions imposed to a lowermost layer in the layer constitution of a light-sensitive material, the amount of coating solution and the viscosity are defined to be 2 to 12 g/m.sup.2 and 1 to 8 cp, respectively (Japanese Unexamined Patent Publication No. 115214/1977), or, in respect of the viscosity .eta..sub.0 of a coating solution for a lowermost layer, when coated at a low shear rate, the scope of tolerance between it and the viscosity .eta..sub.1 of a coating solution for a layer directly above this lowermost 35 layer is defined to be .eta..sub.0 =.eta..sub.1 .+-.10 (cp), and, when coated at a high shear rate, it is defined to be .eta..sub.0 &lt;.eta..sub.1 (Japanese Unexamined Patent Publication No. 108566/1981).
Japanese Patent Publication No. 47045/1976 discloses the importance of the amount of gelatin in a rapid processing, in which, however, the processing time is 60 seconds to 120 seconds in total processing time including the time for gangways. Such a processing time, however, can not satisfy the demands in the ultra rapid processing recently practiced.
Also, in recent years, with increase in medical X-ray examinations in particular, there is a strong demand for decreasing exposed doses not only in the field of medical science but also as an international public opinion. To meet such a demand, there have been used devices or appliances such as fluorescent intensifying paper, intensifying screens, fluorescent screens and X-ray image amplifiers, and a remarkable trend is seen in improvement in these devices or appliances and increase in the sensitivity of X-ray light-sensitive photographic materials. On the other hand, to carry out examinations more precisely, there is a demand for high precision techniques of X-ray photography. Since the precision may proportionally increase with greater X-ray irradiation, an X-ray photographing technique utilizing a larger radiation dose has been developed, and also a large volume X-ray generator has been developed. However, the photographing techniques requiring such a large radiation dose may rather contradict the above demands for decreasing exposed doses, and can not be said to be preferable. Accordingly, in the field of X-ray photographying techniques, it is required to provide a photographic technique that can achieve less exposed doses and yet higher precision. Thus, it has been sought after to develop a photographic material that can obtain a precise image, in other words, a photographic material having higher sensitivity, with less X-ray doses.
Many and various techniques are available for the methods of increasing sensitivity, i.e. sensitizing methods, under the same grain size. It is expected that sensitivity can be increased while keeping the same grain size, namely, while maintaining the covering power, if an appropriate sensitizing technique is used. Many reports have been made on such techniques, including, for example, a method in which a development accelerator such as thioethers is added to an emulsion, a method in which a silver halide emulsion having been spectrally sensitized is subjected to hypersensitization by use of suitable combination of dyes, or an improved technique for optical sensitizers. These methods, however, can not necessarily be said to have general-purpose properties when used in high sensitivity light-sensitive silver halide photographic materials. In other words, the high sensitivity light-sensitive silver halide photographic materials, which are chemically sensitized to an all possible maximum extent, tend to be fogged during storage when the above methods are applied.
Moreover, in the field of X-ray photographs for medical use, recently used are orthochromatic light-sensitive materials which are made light-sensitive in the wavelength region of 540 to 550 nm by carrying out orthochromatic sensitization, rather than regular type materials conventionally having a light-sensitive region at 450 nm. The materials sensitized like this have wide light-sensitive wavelength region and also have a sensitivity made higher. Accordingly, they can decrease exposed X-ray doses and minimize the influence to be given to human bodies. Thus, dye sensitization is a very useful sensitizing means, but is still involved in unsolved problems. For example, there remains a problem that sufficient sensitivity can not be obtained depending on the kind of photographic emulsions to be used.
Pressure desensitization (i.e., desensitization seen at the time of development, caused by mechanical pressure applied before exposure) also may sometimes occur due to various mechanical pressure applied before exposure. For instance, in X-ray films for medical use, which are large in size, film folding such as the so-called knick mark folding may sometimes occur, which is a phenomenon that a film is folded by its own weight at a portion where the film is held, whereby the pressure desensitization is liable to occur. Also, nowadays, automatic exposing and developing apparatus utilizing mechanical conveyance are widely used as medical X-ray photographic systems. In such apparatus, however, mechanical force may be applied to films, whereby the above-mentioned pressure blackening and pressure desensitization tend to occur especially in a dry place as in winter. Such a phenomenon is likely to cause serious difficulties in medial diagnosis. In particular, it is well known that light-sensitive silver halide photographic materials comprising silver halide grains having large grain size and high sensitivity are still more likely to cause the pressure desensitization.
As materials aiming at improving the pressure desensitization, those using thallium or those using a dye are disclosed in U.S. Pat. Nos. 2,628,167, 2,759,822, 3,455,235 and 2,296,204, French Pat. No. 2,296,204, Japanese Unexamined Patent Publications Nos. 107129/1976 and 116025/1975, etc., but the improvement to such a level is insufficient, or dye stains may greatly occur, or other materials can not necessarily be said to have sufficiently derived the nature inherent in the light-sensitive silver halide photographic materials having high sensitivity, comprising large grain size silver halide emulsions and chiefly utilizing ordinary surface sensitivity.
On the other hand, various attempts have been made to decrease the pressure desensitization by changing binder properties of light-sensitive silver halide photographic materials, as disclosed, for example, in U.S. Pat. Nos. 3,536,491, 3,775,128, 3,003,878, 2,759,821 and 3,772,032, and further in Japanese Unexamined Patent Publications No. 3325/1978, No. 56227/1975, No. 147324/1975 and No. 141625/1976, etc. However, although an improvement has been made for the pressure sensitization by these techniques, no fundamental improvement has been achieved as there may seriously occur the sticking of film surfaces or the deterioration of binder properties such as dryness and scratching.